Chain-type door locks typically comprise a door plate which is mounted on a door and a wall plate which is mounted on the wall or door jamb adjacent the door. The plates are generally secured to the door or wall by screws. The chain is fixedly attached at one end to one of the plates, e.g., the door plate, and comprises a key which can be inserted into one end of a slot in the other plate e.g., the wall plate. When the key is moved to the other end of the slot, it cannot be pulled out of the slot when the door is opened. Thus, the door can only be opened to the extent that the chain becomes taut. To open the door completely, the key of the chain must be manually moved to the opposite end of the slot and removed. Such chain-type door locks thereby allow a door to be opened a select distance to provide visual access and some physical access to the person on the other side of the door while preventing the door from being opened past the select distance.
When a chain door lock is engaged and a person attempts to open the door, the chain extending between the door and the wall plate becomes taut and forces are applied to both the door plate and the wall plate. If sufficient pressure is applied against the door, the door and/or wall plates can be pulled or torn off of the door and/or wall. This is particularly true of the wall plate since it tends to be pulled directly away from the wall along the length of the screws. Hence, a drawback to conventional chain-type door locks is that the door plate and particularly the wall plate can be pulled off the door or wall without too much difficulty.